1. Field of the Invention
This invention relates to a process for the production of surface active alkyl glycosides by reacting butanol with a glycose in the presence of a suitable acid catalyst to form a butyl glycoside. The butyl glycoside is then transacetalized with a fatty alcohol containing from 12 to 18 carbon atoms. The products of this invention are surface active and show good biodegradability.
2. Statement of Related Art
In the development of new surface-active substances, which are suitable for use as industrial surfactants for the manufacture of detergents and cleaning preparations, renewable raw materials are being used to an increasing extent for production. Hitherto, oleochemical raw materials, such as for example fatty acids, fatty acid esters and fatty alcohols, have largely been used for this purpose. The object of the efforts being made in this direction is to develop a base independent of petrochemistry and, at the same time, to obtain better products showing environmental compatibility, including good biological degradability. With these aspects in mind, interest has recently been shown in the surface-active alkyl glycosides, which are acetals of sugars and fatty alcohols.
In the context of the invention, alkyl glycosides are understood to be the reaction products of sugars and fatty alcohols, suitable sugar components being the aldoses and ketoses glucose, fructose, mannose, galactose, talose, gulose, allose, altrose, idose, arabinose, xylose, lyxose and ribose, which are referred to hereinafter as glycoses. Particularly preferred alkyl glycosides are alkyl glucosides by virtue of the ready availability of glucose. In its broadest sense, the term "alkyl" in alkyl glycoside is intended to encompass the residue of an aliphatic alcohol, preferably a fatty alcohol, obtainable from natural fats, i.e. saturated and unsaturated residues and also mixtures thereof, including those having different chain lengths. The terms alkyl oligoglycoside, alkyl polyglycoside, alkyl oligosaccharide and alkyl polysaccharide apply to alkylated glycoses of the type in which one alkyl radical in the form of the acetal is attached to more than one glycose residue, i.e. to a polysaccharide or oligosaccharide residue; these terms are regarded as synonymous with one another. Accordingly, alkyl monoglycoside is the acetal of a monosaccharide. Since the reaction products of the sugars and the fatty alcohols are generally mixtures, the term alkyl glycoside is intended to encompass both alkyl monoglycosides and also alkyl poly(oligo)glycosides, providing the particular structural differences are not important.
The surface-active alkyl glycosides essentially containing C.sub.12 -C.sub.18 alkyl or alkenyl radicals belong to the class of nonionic surfactants. However, whereas in standard nonionic surfactants of the alkyl polyglycol ether type, the hydrophobic part emanates from renewable raw materials where it is derived from fatty alcohols, while the hydrophilic part is made up of ethylene oxide units and hence of a petrochemical raw material, the alkyl glycosides as fatty alkyl glycosides may be completely prepared from renewable raw materials, namely fats on the one hand and sugars or starches on the other hand.
Surface-active alkyl glycosides have been known as ingredients in detergents for more than 50 years. Thus, Austrian patent 135,333 describes the production of lauryl glucoside and cetyl glucoside from acetobromoglucose and the particular fatty alcohol in the presence of a base. The direct synthesis from glucose and lauryl alcohol in the presence of hydrogen chloride as an acidic catalyst is also disclosed.
According to the teaching of German patent 611,055, alkyl glucosides can be prepared from penta-acetyl glucose and a fatty alcohol in the presence of anhydrous zinc chloride.
German patent 593,422 describes the maltosides, the lactosides of aliphatic alcohols containing more than 8 carbon atoms and their use as emulsifying, cleaning and wetting agents. For example, the addition of cetyl maltoside to ordinary soap, which at that time was the principal constituent of detergents, was said to improve the detergent effect of the soap. This is explained by the effect of the cetyl maltoside as a calcium soap dispersant.
The sixties and seventies saw several proposals for improved processes for the production of alkyl glycosides either by direct reaction of glycose, generally in the form of glucose, with an excess of the fatty alcohol and an acid as catalyst (direct synthesis) or using a lower alcohol or glycol as solvent and reactant (transacetalization). Thus, U.S. Pat. No. 3,547,828 (Mansfield et al.) describes the production of a ternary mixture of alkyl oligoglucosides, alkyl monoglucosides and the corresponding C.sub.11 -C.sub.32 alkanols by transacetalization with butanol. In this process, the glucose is first reacted with butanol and an acidic catalyst, such as sulfuric acid, to form butyl glucoside. The water of reaction is separated at the reflux temperature. Two to six mols of butanol are used per tool glucose. The fatty alcohol is then added in quantities of 0.5 to 4 tools per mol of glucose and the excess butanol and also the butanol formed during the transacetalization reaction are removed by distillation. The transacetalization reaction is optionally terminated, such that parts of the butyl glycoside remain in the reaction mixture. Products of low viscosity can be prepared in this manner. The acidic catalyst is then neutralized by addition of sodium hydroxide solution. Excess fatty alcohol is then largely removed in vacuo to the required level, generally to less than 2% by weight. For example, lauryl alcohol can thus be removed by distillation under a pressure of 2 mm Hg at a temperature of 150.degree. C. A proportion of alkyl oligoglucoside can be isolated from the resulting 3-component mixture of alkyl monoglucoside, alkyl ol igoglucoside and fatty alcohol, optionally containing proportions of butyl glycoside, by adding acetone to the mixture. The oligoglucosides are insoluble in acetone and can be easily separated.
U.S. Pat. No. 3,450,690 (Gibbons et al.), teaches that unwanted alkali-sensitive, discoloring impurities of alkyl glucosides based on C.sub.1 -C.sub.8 alkanols, prepared by direct synthesis, can be removed from the reaction product by not only neutralizing the acidic catalyst through its addition of inorganic or organic bases, as for example sodium hydroxide, sodium methylate, calcium hydroxide, barium hydroxide, barium methylate or strongly basic organic amines, but also by adjusting the mixture to an alkaline pH value of at least 8, followed by brief heating to temperatures of 50.degree. C. to 200.degree. C. The reaction product is then filtered off and the excess of alcohol is removed. The residual reducing sugar, which is thought to be responsible for the color instability of the untreated product, are alleged to be removed by this treatment.
Another problem arising in the production of surface-active alkyl glycosides based on fatty alcohols containing 12 to 18 carbon atoms lies in the difficulty of separating any such unreacted fatty alcohols by distillation from the reaction product. To this end, it is proposed in European patent application 32 252 (BASF, Klahr et al.) to effect the separation of such unreacted fatty alcohols by distillation in the presence of glycols having boiling points which are at most 10.degree. C. above and at most 30.degree. C. below those of the alcohols to be separated. In this way, the distillation process can be carried out at temperatures no higher than 140.degree. C. under a vacuum of about 8 mbar.
According to the teaching of European patent application 92 875 (Proctor & Gamble) Mao et al. production of long-chain alkyl glycosides utilizing its transacetalization process with butanol can be controlled in such a way that the end product contains a residue of less than 10% by weight of butyl glucosides. The formation of long-chain alkyl oligoglycosides having a relatively high degree of oligomerization, i.e. containing 6 and more glucose units in the molecule, can also be reduced. The products thus obtained consist essentially of alkyl monoglucoside and alkyl oligoglucosides, the content of alkyl monoglucosides being at most 60% by weight and the average degree of oligomerization being from 1.5 to 3. The proportion of short-chain alkyl glucosides, particularly butyl glucosides, is below 10%, while the proportion of unreacted fatty alcohol is said to be below 2%. The use of a thin-layer evaporator is recommended for the removal of the fatty alcohol by distillation.
European patent application 92 876 (Proctor & Gamble, Mao et al.) also describes the production of long-chain alkyl glucosides having a degree of oligomerization of 1.5 to 20 by the transacetalization process with butanol, the transacetalization catalyst (p-toluenesulfonic acid) being inactivated by neutralization when at least 90% of the butyl glucoside has reacted, such that at most 10% butyl glucoside remains in the reaction product. In this case, too, the use of a thin-layer evaporator is recommended for removal of the excess of fatty alcohol. The reaction products are also said to contain less than 60% by weight alkyl monoglucoside and less than 2% free fatty alcohol, In this known production process, a very small excess of fatty alcohol is used to ensure that large quantities of the required alkyl oligoglucoside, i.e. more than 60% by weight, are obtained.
European patent application 96 917 (Procter & Gamble, Farris) describes an improved process for the acid-catalyzed direct synthesis, in which a monosaccharide, preferably glucose, is added to the mixture of fatty alcohol and catalyst continuously or in portions at a temperature of from 80 to 150.degree. C. at such rate that no more than 10% unreacted monosaccharide is present in the reaction mixture. The addition of the monosaccharide is controlled in such a way that a substantially clear phase is always present.
The monosaccharide is preferably used as finely ground powder in admixture with part of the fatty alcohol. As the monosaccharide is added, the water formed is removed by distillation under a reduced pressure of about 0.1 to 300 mm Hg. This process is said to give a product containing 20 to 70% alkyl monoglycoside, less than 10% mono- and polysaccharides, less than 2% free fatty alcohol and, the remainder being alkyl polyglycosides, i.e. essentially di-, tri- and tetraglycosides.
According to European patent application 132 046 (Procter & Gamble, Letton), an organic base which is either the alkali (Na, K, Li), alkaline earth (Ba, Ca) or aluminum salt of a weak low molecular weight acid, for example sodium acetate, or the corresponding alcohol ate, for example sodium ethylate, is used to neutralize the acidic catalyst in a direct synthesis process. A narrow pH value range near the neutral point (pH 6.6 to 7, preferably 6.7 to 6.8) is established.
According to European patent application 132 043 (Procter & Gamble, Davis et al. ), the color quality of the product is improved and the residual polysaccharide in the product is reduced when the acidic catalyst used is the acid form of an anionic surfactant. In the process according to this literature reference, 2 mols of fatty alcohol are preferably used per mol of glucose and pH values of 6.6 to 7 are attained by adjustment in the neutralization of the acid catalyst with sodium hydroxide or sodium carbonate.
To be able to use the alkyl glycosides as surfactant ingredients in detergents and cleaning preparations in commercial scale, two requirements have to be satisfied. First, the alkyl glycosides must be color-stable under alkaline conditions so that they can be used in alkaline formulations. Second, processes for the production of alkyl glycosides must be designed in such a way that the end products can be produced without difficulty in large quantities. Neither of these two requirements is satisfied by known processes or by the properties of the resulting end products.
According to European patent application 77,167 (Rohm & Haas, Arnaudis), the color quality of the surface-active alkyl glycosides may be improved by using a standard acid catalyst together with an acidic reducing agent selected from the group comprising phosphorous acid, hypophosphorous acid, sulfurous acid, hyposulfurous acid, nitrous acid and/or hyponitrous acid, or salts thereof, in the production of the alkyl glycosides.
According to the teaching of European patent application 102, 558 (BASF, Lorenz et al.), light-colored C3-C.sub.5 alkyl glucosides, which may be transacetalized to higher, surface-active alkyl glucosides, are obtained by production in the presence of an acidic catalyst and at least equivalent quantities of an alkali metal salt of a boric acid, preferably sodium perborate.
According to another proposal in European patent application 165 721 (Staley, McDaniel et al.), an aqueous solution of a surface-active alkyl polyglucoside is treated first with an oxidizing agent, (preferably a hydrogen peroxide solution), and then with a sulfur dioxide source, such as an aqueous solution of sodium bisulfite. The products thus obtained are said to remain color-stable, even after prolonged storage.
All known production processes which are concerned with improving the color quality and stability of alkyl glycosides in storage are attended by the disadvantage that, to achieve these improvements, additional chemical agents have to be added either during the production process or by way of aftertreatment of the reaction product.